Search

According to modern atmospheric circulation models, the Intertropical Convergence Zone (ITCZ), as the Earth's meteorological equator, plays an essential role in the low-latitude hydrologic cycles. The limited availability of high-resolution tropical climate archives, especially from the Early Paleozoic Era, severely limits our understanding of ITCZ migration dynamics in deep time. Here we present high-resolution climate-proxy records (i.e., magnetic susceptibility (MS) and Zirconium/Aluminum (Zr/Al)) from tropical marine sediments of the ∼526-million-year-old Qiongzhusi Formation in South China to investigate the link between orbitally forced insolation changes, ITCZ migration dynamics, and low-latitude climate processes. These orbital-scale variations in MS and Zr/Al series are interpreted as alternations between wet and dry cycles, controlled by monsoon intensity under the orbitally forced ITCZ-related paleo-Hadley Cell dynamics. Our results show that combined precession and obliquity orbital cycles had an impact on the Early Cambrian ITCZ migration. Specifically, the precession and obliquity forcing shift the mean position of the ITCZ latitudinally by changing the interhemispheric pressure contrasts, thus affecting the low latitude hydroclimate cycle. We report semi-precession cycles of 8.3–7.9 kyr, which were probably associated with the twice-annual passage of the ITCZ across the intertropical zone, consistent with the paleogeographical location of South China near the equator during the Early Cambrian. Observed ∼1.1 – ∼1.5 Myr eccentricity amplitude modulation (AM) cycles and ∼ 1.0 – ∼1.2 Myr obliquity AM cycles may provide geological evidence for the chaotic motion between Earth and Mars in the Early Cambrian. • Combined precession and obliquity cycles regulated the Early Cambrian ITCZ migration. • We report the semi-precession cycles of 7.9–8.3 kyr in the Early Cambrian. • Our study provides geological evidence for the chaotic Solar System in the Early Cambrian. [ABSTRACT FROM AUTHOR]

• We develop a 10.8-Myr astronomical time scale for the Early Cambrian Stage 2-Stage 3. • ∼1.5-Myr obliquity cycles significantly affect sea-level oscillations in the greenhouse period. • New chaotic resonance of Mars-Earth system may occur in the Early Cambrian Period. • Constraints on the Earth-Moon system evolution in deep time are refined. The early Cambrian was a critical period of Earth history, marked by explosive diversification of metazoans and several profound changes in Earth's surface environments and global climate. A valid temporal framework for the early Cambrian Period and across the major bio-events is poorly constrained, and the key underlying forcings of million-year (Myr) scale sea-level variations in a greenhouse lacking polar ice sheets are still disputed. Here, the high-resolution gamma-ray logs (GR) and Fe/Al records are utilized to conduct cyclostratigraphic analysis of the early Cambrian Stage 2-Stage 3 Qiongzhusi Formation of the Well A borehole in South China. A ∼10.8 Myr-long high-resolution astronomical time scale across Stage 2-Stage 3 is developed by astronomical tuning of gamma-ray logs and Fe/Al series to the stable 405-kyr long-eccentricity cycles. The Myr-scale sea-level fluctuations in the early Cambrian greenhouse are reconstructed through the sedimentary noise modeling of the 405-tuned GR series and agree with sequence stratigraphic interpretations, lithofacies stacking patterns, and depositional environment changes. The antiphase correlation of filtered ∼1.5 Myr cycles of sedimentary noise curves with the ∼1.5 Myr obliquity modulation cycles demonstrates that the variations in land-ocean water exchange linked to changes in poleward moisture and heat transport dominated by ∼1.5 Myr obliquity modulation cycles may be a primary driver for eustasy during non-glacial early Cambrian period. A new resonance state in the early Cambrian Stage 2-Stage 3, manifested by ∼1.5 Myr eccentricity: ∼1.5 Myr obliquity, could be mainly associated with the Earth-Mars secular resonance and constrain the chaotic evolution of the Solar System in deep time. Two independent approaches are employed to reconstruct the history of Earth-Moon system characteristics, including the precession constant, the Earth-Moon distance and the day length. Our results enhance knowledge of the connection of Myr-scale sea-level variations to astronomically induced climate change under greenhouse climate and provide new empirical constraints on the chaotic motion of the Solar System and the evolution of the Earth-Moon System in deep time. [ABSTRACT FROM AUTHOR]